COMP Cams Valve Lock 5/16in Single Groovelock angle and 5 16" valve stem size is a perfect replacement lock for stock engine rebuilds. It is recommended only for street Applications with lighter valve spring loads. It is critically important to make sure valve locks match the valve size. There should always be a small gap between the two halves of the lock when they are properly positioned on the valve stem. If the two halves fit together without a gap, they are too large. If the locks fit